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Calavera

Boost gets in very late - help!

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Hello together,

 

at my Esprit Turbo SE (MY90) - I have a problem with the turbo boost - it takes in very, very late at about >5.000U/min then it raises to about 0.5 to 0.7 bar and the car pushes forward as it should.

 

But with U/min under 5k the boost presure stays at a maximum of about 0.1 bar...

 

We meanwhile:

 

- changed the waste-gate actuator (new one) and checked the right position of it
- removed the kat (exhaust) to see the open turbo - the waste gate valve sits perfect in its seat and the turbine looks good as well - don´t think there´s the problem.

 

Do you have any ideas where to look at next? Is there any sensor to check which maybe takes effect at the turboboost which maybe is gone?

 

I think I had a similar problem before when the engine was completely cold - sometimes I had no boost availible here to but the problem was gone just when the engine warmed up... so maybe any sensor which was not right fixed or was faulty is no gone complete???

 

Please help!

 

Many thanks for any idea!!!!

Calavera

Edited by Calavera

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Boost will be limited if temperature is low.  Do you have Freescan?  You need to check your coolant temp sensor.  It could be numerous other things but your post suggests you should look here first.

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Hi - no unfortunaly no freescan - seems as if I should check out how it works ... ;)

 

Before I search all the documentation up and down - can you give me a hint where the coolant sensor sits?

 

And thanks!!!

Calavera

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It's under the inlet manifold, roughly between ports 3 and 4.  Quite difficult to get at but possible to change it with a deep socket.  It's a GM part, so should be available from a decent parts store.

 

Be very careful not to disturb any other cables whilst changing this.

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Thanks!!! will check it!

 

Any other possible idea´s are welcome - cause I can test it not before next week (due to my neightbors Garage ;) ) So if we once start would be great to check as much possible reasons as we can at one time...

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Hi - do you think a broken actuator for the exhaust back pressure valve could have the same effect? @sparky - the sensor you mentioned should give the signal for it - right? As I read in the repair handbook the e.b.p.v. should open at water temperatures higher then 70° - so maybe the actuator is defective?   

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Wire the EBPV open, you don't need it to work and it's one less thing to go wrong.

 

Is your cat in good condition too, no bits missing or blocking the core as you looked into it?

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@Bibs - yes we will check it! The cat should be o.k. - no bits missing - but we didn´t look into when disconected... probably because the lambda sensor was fixed and we didn´t took it out completely - hmm - we better should...

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Certainly looks like the one!

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Hi guys,

 

just want to let you konw that it was the backpressure valve... man! never thought it has such a big effect...

 

Well after checking:

 

- wast gate actuator (new one!)

- correct closing of the waste gate in its seat
- O2 sensor with freescan

- temperature sensor with freescan

 

the BPV and a leak in the pressure system was left to check... - when we activated the BPV manualy with running engine - the car became at once double as loud as before ;) (had´nt the correct loundness present after the winter break) and while the following test-drive the boost gets in again just from 2000 revs up...

 

Back on road again - yea!

 

Thanks for you advice!

Regards

 

Calavera

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Hello - just another question to all SE, S4, S4S or S300 Drivers...

 

After fixing the backpressure valve my boot raises very fast again - but as I think maybe too high?!? If I kickdown the pedal the boost raises shortly up to 1,1 or 1,2 bar and then falls back to 1,0 or 0,8 depending if boost mode is active or not...

 

I don´t know if that behavior is the same as before we changed the wastgate actuator and fixed the backpressure valve...

 

Is this behavior normal or shouldn´t raise the boostmeter over the 1,0bar mark?

 

If I press the pedal slower and constantly the boost goes up to 0,8 or 1,0 and stays there - the "overboost" only appears if I kickdown... - don´t want to damage the engine!

 

Thanks!

Calavera

Edited by Calavera

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Double check your wastegate adjustment.  Though if boost rises too much, then the ECU should reduce boost to ~.65bar by the boost control freq valve.

 

BTW, at my altitude of 5300ft+, my boost gauge pegs often.  What is your altitude?

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Hi

 

Do anyone have doc. how to adjust the westgate. I think i might as well get to much pressure to early.

Anyone have a FreScann log with all working fine. I have the SE version with 264 hp.

 

Regards Tom

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My 1990 SE does the same thing, boost only up to 0,5 bar on the gauge, sometimes it goes a tad behind 0,5 bar. I will check the back pressure valve today as I ve seen that the vacuum port is not hooked up.

 

Oh and its also very quiet ^^

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So after work I did a quick check on the backpressure valve, its not hooked up and per default in the closed position. Going to fix this tomorrow, then its due for a photo shooting :)

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